The synthesis of self-assembled polycrystalline 1-D CuO nanostructures in aqueous medium and a study of their multifunctional features

Abstract

In the present work a wet chemical method has been employed for the synthesis of self-assembled 1-D polycrystalline nanochains of CuO. The Zetasizer, AFM, FESEM and TEM results show that in the grown sample the CuO nanoparticles become organized to form chain like structures. These chains have an average size of NPs and chain length of ~25 ± 7 nm and 495 ± 135 nm, respectively. The CuO nanochains have a band gap of 2.7 eV and upon 340 nm irradiation exhibit a characteristic fluorescence spectrum peaking at 410 nm along with two shoulders at higher (390 nm, 3.2 eV) and lower energies (440 nm, 2.8 eV). The fluorescence lifetime is observed to increase with the decreasing energy of emission. These nanostructures exhibit three red shifted Raman bands at 286, 335 and 619 cm⁻¹, compared to the bulk CuO. The magnetic measurements show a weak ferromagnetic interaction at room temperature which is enhanced further at lower temperatures associated with an exchange bias effect (H_eb = 290 Oe) and spin glass like behavior (at 56 K). At room temperature CuO nanochains demonstrate a weak ferroelectric behavior along with a high dielectric constant of the order of >10³ at low frequency. The optical, Raman and magnetic measurements suggest a relatively stronger quantum confinement and the presence of defects in the as synthesized CuO nanochains. Morphological changes leading to the creation of defects appear to be responsible for the observed changes in their optical, magnetic and ferroelectric properties. The correlation between the morphology and the observed optical, magnetic and ferroelectric properties of the samples has been analyzed.